At first I thought it was something to do with Chris' maxframes config that I was using but now it seems to be happening without it, so I'm very perplexed.

I have a pretty powerful PC and can hold on to 242fps easily, but sometimes when I launch the game, my CPU usage will be low and my GPU usage will be high and the game will chug and run really badly (60-70fps and feels like lots of mouselag). When the framerate is high the CPU usage is a lot higher and GPU usage is only at a few percent (the way it's supposed to be, surely?)

Anyone else experienced this? Like I said it's really intermittent and sometimes it will be fine and sometimes not. Restarting TF2 normally fixes it but then next time I launch it might go back to running like shit again.

Hawbagz

If the game seems to stutter and assuming you have the frame rate limiter active, try disabling it (fps_max 0).

Obviously that might not be what you want for a long term solution, but it seems to cause occasional performance problems for some users. I've ran into it on my machine, but it usually only happened at the start of a round (usually the first one after a map change) and went away within a minute.